Business Segments and Revenue from Contracts with Customers - Schedule of Segment Results and Reconciliation (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Segment Reporting Information [Line Items]
Net interest income	$ 5,791	$ 5,718
Non-interest income	1,292	1,191
Total net revenue	7,083	6,909
Provision (benefit) for credit losses	1,693	1,674
Total non-interest expense	3,671	3,573
Income (loss) from continuing operations before income taxes	1,719	1,662
Income tax provision (benefit)	309	319
Income (loss) from continuing operations, net of tax	1,410	1,343
Loans held for investment	240,273	248,256	$ 245,899
Total Deposits	255,107	250,847	$ 249,764
Operating segments | Credit Card
Segment Reporting Information [Line Items]
Net interest income	3,590	3,558
Non-interest income	950	857
Total net revenue	4,540	4,415
Provision (benefit) for credit losses	1,389	1,456
Total non-interest expense	2,171	2,039
Income (loss) from continuing operations before income taxes	980	920
Income tax provision (benefit)	229	213
Income (loss) from continuing operations, net of tax	751	707
Loans held for investment	109,836	107,576
Total Deposits	0	0
Operating segments | Consumer Banking
Segment Reporting Information [Line Items]
Net interest income	1,679	1,615
Non-interest income	160	174
Total net revenue	1,839	1,789
Provision (benefit) for credit losses	235	233
Total non-interest expense	994	1,000
Income (loss) from continuing operations before income taxes	610	556
Income tax provision (benefit)	142	130
Income (loss) from continuing operations, net of tax	468	426
Loans held for investment	59,248	74,674
Total Deposits	205,439	193,073
Operating segments | Commercial Banking
Segment Reporting Information [Line Items]
Net interest income	489	506
Non-interest income	187	187
Total net revenue	676	693
Provision (benefit) for credit losses	69	(14)
Total non-interest expense	417	403
Income (loss) from continuing operations before income taxes	190	304
Income tax provision (benefit)	44	71
Income (loss) from continuing operations, net of tax	146	233
Loans held for investment	71,189	65,953
Total Deposits	31,248	34,449
Revenue change due to impact of federal tax rate		30
Other
Segment Reporting Information [Line Items]
Net interest income	33	39
Non-interest income	(5)	(27)
Total net revenue	28	12
Provision (benefit) for credit losses	0	(1)
Total non-interest expense	89	131
Income (loss) from continuing operations before income taxes	(61)	(118)
Income tax provision (benefit)	(106)	(95)
Income (loss) from continuing operations, net of tax	45	(23)
Loans held for investment	0	53
Total Deposits	$ 18,420	$ 23,325